Deciphering why Salmonella Gallinarum is less invasive in vitro than Salmonella Enteritidis

International audienceSalmonella Gallinarum and Salmonella Enteritidis are genetically closely related however associated with different pathologies. Several studies have suggested that S. Gallinarum is less invasive in vitro than S. Enteritidis. In this study we confirm that the S. Gallinarum strains tested were much less invasive than the S. Enteritidis strains tested in cells of avian or human origin. In addition, the S. Gallinarum T3SS-1-dependent ability to invade host cells was delayed by two to three hours compared to S. Enteritidis, indicating that T3SS-1-dependent entry is less efficient in S. Gallinarum than S. Enteritidis. This was neither due to a decreased transcription of T3SS-1 related genes when bacteria come into contact with cells, as transcription of hilA, invF and sipA was similar to that observed for S. Enteritidis, nor to a lack of functionality of the S. Gallinarum T3SS-1 apparatus as this apparatus was able to secrete and translocate effector proteins into host cells. In contrast, genome comparison of four S. Gallinarum and two S. Enteritidis strains revealed that all S. Gallinarum genomes displayed the same point mutations in each of the main T3SS-1 effector genes sipA, sopE, sopE2, sopD and sopA

DNA vaccination against Chlamydiaceae: current status and perspectives

DNA vaccination (also called genetic vaccination) recently celebrated its ten years of existence. This new method of immunization presents several advantages, including the induction of both humoral and cellular immune responses. This vaccination strategy has been very successful and has served as a basis for numerous experiments that had the aim of resolving parasitic, viral, and bacterial infections. In particular, DNA vaccination has been evaluated against Chlamydiaceae, small obligate intracellular bacteria, that induce many pathologies in humans and animals. Despite promising protective effects obtained in murine and turkey models with genes encoding outer membrane proteins and heat shock proteins, DNA vaccination against Chlamydiaceae must be optimized by further investigations and could benefit from the genomic sequencing in terms of the identification of new antigens

Protection evaluation against Chlamydophila abortus challenge by DNA vaccination with a dnaK-encoding plasmid in pregnant and non-pregnant mice

Mice were intramuscularly immunized with a dnaK-encoding DNA plasmid. The protective effect of DNA immunization against Chlamydophila abortus infection was studied in pregnant and non-pregnant mice models. In non-pregnant mice, the dnaK vaccine induced a specific humoral response with the predominant IgG2a isotype, which failed to have in vitro neutralizing properties. No delayed-type hypersensitivity reaction was observed and the spleens of dnaK vaccinated-mice were not protected against C. abortus challenge. In pregnant mice, the dnaK vaccine induced a non-specific partial protection from abortion. This may be due to the immunogenic properties of the CpG motifs of bacterial DNA present in the vaccinal plasmid backbone. Nevertheless, spleens of dnaK vaccinated-pregnant mice were not protected.Évaluation de la protection induite par vaccination ADN avec un plasmide codant pour dnaK contre une épreuve par Chlamydophila abortus chez des souris gestantes ou non-gestantes. Des souris ont été immunisées par l'injection intramusculaire d'un plasmide codant pour la protéine DnaK. L'effet protecteur de la vaccination ADN contre une infection par Chlamydophila abortus a été évalué dans des modèles de souris gestantes ou non-gestantes. La vaccination ADN avec le gène dnaK induit une réponse humorale spécifique chez les souris non-gestantes avec une prédominance d'IgG2a qui n'ont pas présenté d'activité neutralisante in vitro. Aucune réaction d'hypersensibilité retardée n'a été observée et les rates des souris vaccinées avec le vaccin ADN-dnaK n'ont pas été protégées contre l'infection par C. abortus. Chez les souris gestantes, le vaccin ADN-dnaK réduit partiellement et de façon non spécifique les avortements. Les îlots CpG de l'ADN bactérien, connus pour leur propriétés immunogéniques, pourraient être responsables de cet effet protecteur non spécifique. Cependant, aucune élimination des bactéries n'a été observée dans les rates des souris gestantes

Proteic boost enhances humoral response induced by DNA vaccination with the dnaK gene of Chlamydophila abortus but fails to protect pregnant mice against a virulence challenge

In order to enhance the quantity and the protective properties of the antibodies induced by DNA vaccination with the heat shock protein dnaK gene of Chlamydophila abortus AB7 as well as to elicit an efficient cellular immune response, we vaccinated mice with a DNA prime followed by a boost with the recombinant DnaK protein. In non-pregnant mice, this strategy induced the same predominance of the IgG2a isotype as DNA immunization alone with a substantial increased antibody level. The induced antibodies had no in vitro neutralizing properties on C. abortus infectivity. Moreover, the proteic boost probably failed to elicit an efficient cellular immune response since the pregnant or non-pregnant mice were not protected against the bacterial challenge

Proteic boost enhances humoral response induced by DNA vaccination with the dnaK gene of Chlamydophila abortus but fails to protect pregnant mice against a virulence challenge

In order to enhance the quantity and the protective properties of the antibodies induced by DNA vaccination with the heat shock protein dnaK gene of Chlamydophila abortus AB7 as well as to elicit an efficient cellular immune response, we vaccinated mice with a DNA prime followed by a boost with the recombinant DnaK protein. In non-pregnant mice, this strategy induced the same predominance of the IgG2a isotype as DNA immunization alone with a substantial increased antibody level. The induced antibodies had no in vitro neutralizing properties on C. abortus infectivity. Moreover, the proteic boost probably failed to elicit an efficient cellular immune response since the pregnant or non-pregnant mice were not protected against the bacterial challenge

Regulation of the pefI-srgC operon involved in adhesion and invasion of Salmonella Typhimurium by the transcriptional regulator of quorum sensing SdiA

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Regulation of the <em>pefl-srgC</em> operon involved in adhesion and invasin of <em>Salmonella</em> Tiphimurium by the transcriptional regulator of quorum sensing SdiA

National audienc

An Updated View on the Rck Invasin of Salmonella: Still Much to Discover

Salmonella is a facultative intracellular Gram-negative bacterium, responsible for a wide range of food- and water-borne diseases ranging from gastroenteritis to typhoid fever depending on hosts and serotypes. Salmonella thus represents a major threat to public health. A key step in Salmonella pathogenesis is the invasion of phagocytic and non-phagocytic host cells. To trigger its own internalization into non-phagocytic cells, Salmonella has developed different mechanisms, involving several invasion factors. For decades, it was accepted that Salmonella could only enter cells through a type three secretion system, called T3SS-1. Recent research has shown that this bacterium expresses outer membrane proteins, such as the Rck protein, which is able to induce Salmonella entry mechanism. Rck mimics natural host cell ligands and triggers engulfment of the bacterium by interacting with the epidermal growth factor receptor. Salmonella is thus able to use multiple entry pathways during the Salmonella infection process. However, it is unclear how and when Salmonella exploits the T3SS-1 and Rck entry mechanisms. As a series of reviews have focused on the T3SS-1, this review aims to describe the current knowledge and the limitations of our understanding of the Rck outer membrane protein. The regulatory cascade which controls Rck expression and the molecular mechanisms underlying Rck-mediated invasion into cells are summarized. The potential role of Rck-mediated invasion in Salmonella pathogenesis and the intracellular behavior of the bacteria following a Salmonella Rck-dependent entry are discussed

Mechanism of transcriptional regulation of rck, encoding an invasin of <em>Salmonella typhimurium</em>, by the quorum sensing regulator SdiA

International audienc

New insights concerning the distribution of Salmonella virulence factor Rck

International audienceSalmonella are facultative intracellular bacteria able to infect a broad range of hosts using several virulence factors, including the Rck outer membrane protein. This protein is responsible for (i) resistance to complement, in particular through membrane attack complex formation inhibition, (ii) bacterial adhesion, through laminin binding, and (iii) host-cell invasion, through a Zipper-like mechanism following interaction with the EGF-R. The rck ORF belongs to the pefI-srgC operon, carried on the virulence plasmid of Salmonella. Currently, rck has only been characterized on the virulence plasmid of three serovars, i.e. Enteritidis, Typhimurium and Bovismorbificans. As the literature suggested a larger distribution, our aim was to study the prevalence of the rck ORF in the genus Salmonella taking advantage of the large online database Enterobase and of its experimental data associated (e.g. in silico serovars prediction, wgMLST sequence type). 188,233 genomes belonging to more than 471 Salmonella serovars were analyzed. Our results revealed the presence of the rck gene in 39 serovars and a predominance of some alleles for some serovars. They also suggest that the gene might not be exclusively carried on plasmids. Finally, despite a relatively high number of haplotypes, amino acid sequences comparison revealed a strong conservation of the protein sequences, as the majority of the identified variants showed only minor sequence variations with the three currently described Rck proteins. In conclusion, Rck is more widely distributed in Salmonella serovars than previously expected and consequently could play a role in the virulence of all these serovars